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      <h2><a href="./">Go by Example 中文版</a>: 数字解析</h2>
      
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            <p>从字符串中解析数字在很多程序中是一个基础常见的任务，
而在 Go 中，是这样处理的。</p>

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            <a href="http://play.golang.org/p/UUwBWhO39b6"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
          <div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>

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            <p>内建的 <code>strconv</code> 包提供了数字解析能力。</p>

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          <div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
    <span class="s">&quot;fmt&quot;</span>
    <span class="s">&quot;strconv&quot;</span>
<span class="p">)</span>
</pre></div>

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          <div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>

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            <p>使用 <code>ParseFloat</code>，这里的 <code>64</code> 表示解析的数的位数。</p>

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          <div class="highlight"><pre>    <span class="nx">f</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nx">ParseFloat</span><span class="p">(</span><span class="s">&quot;1.234&quot;</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">f</span><span class="p">)</span>
</pre></div>

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            <p>在使用 <code>ParseInt</code> 解析整型数时，
例子中的参数 <code>0</code> 表示自动推断字符串所表示的数字的进制。
<code>64</code> 表示返回的整型数是以 64 位存储的。</p>

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          <div class="highlight"><pre>    <span class="nx">i</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nx">ParseInt</span><span class="p">(</span><span class="s">&quot;123&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">i</span><span class="p">)</span>
</pre></div>

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            <p><code>ParseInt</code> 会自动识别出字符串是十六进制数。</p>

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          <div class="highlight"><pre>    <span class="nx">d</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nx">ParseInt</span><span class="p">(</span><span class="s">&quot;0x1c8&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">d</span><span class="p">)</span>
</pre></div>

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            <p><code>ParseUint</code> 也是可用的。</p>

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          <div class="highlight"><pre>    <span class="nx">u</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nx">ParseUint</span><span class="p">(</span><span class="s">&quot;789&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">u</span><span class="p">)</span>
</pre></div>

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            <p><code>Atoi</code> 是一个基础的 10 进制整型数转换函数。</p>

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          <div class="highlight"><pre>    <span class="nx">k</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nx">Atoi</span><span class="p">(</span><span class="s">&quot;135&quot;</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">k</span><span class="p">)</span>
</pre></div>

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            <p>在输入错误时，解析函数会返回一个错误。</p>

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          <div class="highlight"><pre>    <span class="nx">_</span><span class="p">,</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nx">Atoi</span><span class="p">(</span><span class="s">&quot;wat&quot;</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">e</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>

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          <div class="highlight"><pre><span class="gp">$</span> go run number-parsing.go 
<span class="go">1.234</span>
<span class="go">123</span>
<span class="go">456</span>
<span class="go">789</span>
<span class="go">135</span>
<span class="go">strconv.ParseInt: parsing &quot;wat&quot;: invalid syntax</span>
</pre></div>

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            <p>下面我们将了解一下另一个常见的解析任务：URL 解析。</p>

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      <p class="next">
        下一个例子: <a href="url-parsing">URL 解析</a>
      </p>
      
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